CMOS image sensors are continually being improved in different ways.
A first issue in CMOS image sensors is fill factor. Increasing pixel fill factor leads to desirable increases in pixel sensitivity and/or full well. An improvement in fill factor can also be traded off with reduced pixel size while retaining the same fill factor.
Primary methods of improving fill factor have been, using backside illumination technology, moving to a smaller geometry process, and sharing components of a pixel across several pixels.